Heat exchangers of the type used for radiators in vehicle engine cooling systems or condensers in vehicle air conditioning systems utilize tubes carrying a coolant or refrigerant and fins between the tubes to effectively increase the contact with air for heat transfer to the air. Often louvers are incorporated in the fins to improve the heat transfer efficiency and thereby decrease the necessary core size. For example, the U.S Pat. No. 2,006,649 to Modine shows a heat exchanger having a plurality of parallel tube, either flat or round, and fins surrounding the tubes. The fins take several configurations including flat fins with louvers The U.S. Pat. No. 3,250,325 to Rhodes, et al., shows a heat exchanger with corrugated fins between adjacent tubes and louvers in the fins disposed between the tube but spaced somewhat from the tubes. Typically, compact heat exchangers utilize extended fin surface area to increase spatial efficiency with the heat transfer performance tending to be enhanced as the fin density increased provided sufficient working fluid (air) mass flow rate is maintained across the extended fin surface. As seen in the above louvered fin designs, various arrangements of consecutive multiple louvers have been utilized to create turbulence in the working fluid; the theory being that such added turbulence increases the convection heat transfer coefficient resulting in increased heat transfer by insuring maximum temperature differential between the extended surface and the working fluid (air). Although the louvers do increase the heat transfer performance of an extended surface fin at a constant air mass flow rate, such increase is typically gained at the expense of air pressure drop.
In U.S. Pat. No. 4,693,307 to Scarseletta, which is incorporated herein by reference, it is revealed that particular fin arrangements can be used to take advantage of both plain fin designs and louvered designs to have both high heat transfer performance and low air side pressure drop at a constant air mass flow. According to that patent, a tube and fin heat exchanger like that shown in FIG. 1 can be equipped with hybrid fins having louvered sections separated by plain fin sections as shown in FIGS. 2 and 3.